Low reluctance resonant structure in waveguide for isolating dc magnetic fields

ABSTRACT

The deleterious interaction of DC magnetic fields, where closely spaced, latching ferrite, waveguide circulators are employed, is overcome by the placement of a magnetic shield in the waveguide between the circulators.

United States Patent [72] lnventors Wieslaw W. Siekanowicz Trenton; Thomas E. Walsh, Kearny; Donald J. Blattner, Princeton, all of [2]] Appl. No. 808,245

[22] Filed Mar. 18, 1969 [45] Patented June l, 1971 [73] Assignee Radio Corporation of America [54] LOW RELUCTANCE RESONANT STRUCTURE IN WAVEGUIDE FOR ISOLATING D.C. MAGNETIC FIELDS 8 Claims, 3 Drawing Figs.

[52] U.S.Cl 333/L1, 333/98 [51] lnt.Cl H0lp 1/32,

HOlp 5/00, H0lf27/36 [50] Fieldoi'Search ..333/l.1,98; 336/84; 335/177, 206, 207, 236, 301, 304, Cursory [56] References Cited UNITED STATES PATENTS 928,204 7/l909 Lawton 336/84X 3,466,571 9/l969 Jansen et al. 333/l.l

Primary ExaminerHerman Karl Saalbach Assistant Examiner-Paul L. Gensler Attorney-Edward J. Norton ABSTRACT: The deleterious interaction of DC magnetic fields, where closely spaced, latching ferrite, waveguide circulators are employed, is overcome by the placement of a magnetic shield in the waveguide between the circulators.

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LOW RELUCTANCE RESONANT STRUCTURE IN WAVEGUIDE FOR ISOLATING D.C. MAGNETIC FIELDS This invention relates to a magnetically shielded waveguide and more particularly to a waveguide having a magnetic shield within the waveguide to prevent a DC (direct current) magnetic field at one end of the waveguide from coupling to the opposite end of the waveguide.

Latching ferrite circulators are well known in the art. A description of such circulators may be found in U.S. Pat. No. 3,350,663 by Siekanowicz et al. The circulators are tuned so that when the ferrite is at tee remanent state, the impedance of the ferrite matches the impedance of the waveguide. when such latching ferrite circulators are closely spaced to one another, such as when a plurality of latching circulators are arranged in series to provide isolation, the circulators become difficult to tune. It has been found that this difficulty in tuning is due to the DC (direct current) magnetic field used to latch one circulator being coupled across the adjacent circulator. The stray field causes a change in the impedance of the ferrite, making it extremely difficult to tune the adjacent circulator. This is particularlya problem when using a latching device wherein the ferrite material is a low coercive force ferrite.

it is an object of the present invention to overcome the difficulties in tuning closely spaced ferrite components.

Briefly, this and other objects of the present invention are provided by a structure of the type presenting a low reluctance magnetic path to DC magnetic fields placed in a waveguide so as to obscure a majority of the inner aperture of the waveguide. The magnetic shield is arranged also to provide coupling of RF signals through the shield that are at the operating RF frequency of the signal coupled to the waveguide.

A detailed description follows in conjunction with the accompanying drawings wherein:

FIG. 1 isa block diagram of a transmit-receive switch and isolator system,

FIG. 2 is a perspective view of two closely spaced waveguide junction circulators, and

FIG. 3 is a cross sectional view of the toroid in FIG. 2.

Referring now to FIG. 1, there is shown a transmit-receive switching system 10. The system includes four circulators ll, 12, 13 and 14.Circulators 12, 13 and 14 are switchable circulators and provide additional isolation of the receiver 15 from the transmitter 16. in the receive mode, a pulse from the driver 17 switches the circulators 12, 13 and 14 to provide low attenuated coupling of signal received at the antenna in the direction of the solid arrows to the receiver 15. In the transmit mode, a pulse from the driver 17 switches the circulators to provide high attenuation coupling, about db. per stage, in the direction of the solid arrows and low attenuation coupling in the direction of the dashed arrows to loads 18, 19 and 20. ln this type of arrangement it is desirable and necessary in certain applications that these circulators be close to each other.

Referring now to FIG. 2 there is shown two switchable waveguide circulators 20 and 21 which are like those shown schematically in FIG. 1. Circulator 20 comprises three waveguide transmission sections 23, 24 and 25 which extend from a common junction region 26. At the center of the common junction region 26 is located a latchable ferrite toroid 30.

Referring to FIG. 3 there is shown toroid 30 comprising a center ferrite post 31, an outer ferrite ring 32 and ferrite discs 33, 34. A latching wire 36 passes through the ferrite toroid 30 and loops around the central post 31 of the ferrite toroid 30. The second ferrite circulator 21 may be similar to the first switchable ferrite circulator 20 or may be a nonswitchable circulator like circulator 11 in FIG. 1. The circulator 21 includes three transmission lines 43, 44 and 45 which extend from a common waveguide region 46. A ferrite toroid 40 is located in the center of the common region 46 and may likewise have a latching wire 47 which passes through the ferrite toroid looping around the center region of the toroid 40 as shown in FIG. 3. Thelatching wires 47 and 36 are each coupled to a current driver, which upon the application of a pulse from the driver,

causes a DC magnetic field to be applied across the ferrite toroid perpendicular to the waveguide as indicated by arrows 50 and 51. Tuning screws 53, 54 and 55 are used to tune the waveguide sections 23, 24 and 25 so that when the ferrite toroid 30 is at the remanent state, the impedance of the ferrite matches that of the waveguide sections. Likewise, tuning screws 56, 57 and 58 are used to tune the waveguide sections 43, 44 and 45 so that when the ferrite toroid 40 is at the remanent state, the impedance of the ferrite matches that of the waveguide sections Waveguide transmission lines 45 and 23 are connected to one another at point 59. A resonant iris 60 of soft iron which obscures over percent of the inner cross section of the common waveguide section as shown in FIG. 2 is positioned at point 59 between the circulators 20 and 21. As shown in FIG. 2, the resonant iris is made of a soft iron so as to act as a low reluctance path to the DC magnetic field across the waveguide and consequently acts as a DC magnetic shield to the DC field used to switch the respective circulators. In this manner the DC magnetic bias field in one circulator is isolated from the other circulator. The resonant iris 60 is arranged to be resonant at the operating radio frequencies of the signals coupled to the circulators. The iris 60 is coated with a silvered surface to lower the insertion loss of the iris. In the operation of the disclosed circulators, the DC magnetic field produced by the flux driver at one circulator is blocked from the adjacent circulator by the magnetic shield provided by the soft iron. The nature of the iris allows microwaves at resonance to pass through with low attenuation. Also, when one of the legs of the circulator is coupled to the transmitter, which may include a magnetron, the second harmonic of the magnetron is blocked from the receiver by the resonant iris.

In accordance with the present invention the above circulators may likewise be any of the known microwave waveguide devices which are closely placed to one another and might have their DC biasing fields coupled to either the ferrimagnetic or ferromagnetic materials. The generic term for both ferrimagnetic or ferromagnetic materials as used herein is gyromagnetic materials. For a further description of such materials see Microwave Ferrites and Ferrimagnetic by Lax and Button, published by McGraw-Hill in 1962.

What I claim is:

l. in a waveguide having an aperture bounded by conductive walls for providing the coupling of radio frequency signals from a first end thereof to a second end thereof where it is desirable to isolate DC magnetic fields at said first end from said second end, the improvement comprising:

a structure of the type presenting a low reluctance magnetic path to said DC magnetic field covering a major cross sectional area of a portion of said inner aperture of the waveguide between said first and second ends to isolate said DC magnetic fields, said structure being arranged to provide resonant coupling of signals at said radio frequency.

2. The combination as claimed in claim 1 wherein said structure has at least one aperture therein resonant at said radio frequency.

3. The combination as claimed in claim 1 wherein the material of said structure is soft iron.

4. in combination:

a first and second waveguide device each operable over a given frequency range and each of the type including a piece of gyromagnetic material located in the waveguide which in response to a DC magnetic field bias, controls the propagation of electromagnetic waves through the device,

said first and second devices coupled together by means of a common waveguide section,

said waveguide section including a resonant iris resonant at the operating frequency of said devices and being of a material to act as a DC magnetic shield to said DC magnetic field.

5. The combination as claimed in claim 4 wherein said first and second devices are circulators.

nant iris is soft iron 8. The combination as claimed in claim 7 wherein said soft iron is silver plated. 

1. In a waveguide having an aperture bounded by conductive walls for providing the coupling of radio frequency signals from a first end thereof to a second end thereof where it is desirable to isolate DC magnetic fields at said first end from said second end, the improvement comprising: a structure of the type presenting a low reluctance magnetic path to said DC magnetic field covering a major cross sectional area of a Portion of said inner aperture of the waveguide between said first and second ends to isolate said DC magnetic fields, said structure being arranged to provide resonant coupling of signals at said radio frequency.
 2. The combination as claimed in claim 1 wherein said structure has at least one aperture therein resonant at said radio frequency.
 3. The combination as claimed in claim 1 wherein the material of said structure is soft iron.
 4. In combination: a first and second waveguide device each operable over a given frequency range and each of the type including a piece of gyromagnetic material located in the waveguide which in response to a DC magnetic field bias, controls the propagation of electromagnetic waves through the device, said first and second devices coupled together by means of a common waveguide section, said waveguide section including a resonant iris resonant at the operating frequency of said devices and being of a material to act as a DC magnetic shield to said DC magnetic field.
 5. The combination as claimed in claim 4 wherein said first and second devices are circulators.
 6. The combination as claimed in claim 4 wherein more than half of the cross sectional area of a portion of said waveguide is obscured by said resonant iris.
 7. The combination as claimed in claim 6 wherein said resonant iris is soft iron.
 8. The combination as claimed in claim 7 wherein said soft iron is silver plated. 